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General HD (720 / 1080) Acquisition
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Old May 14th, 2005, 12:46 AM   #16
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True enough Douglas. My point was not to just go by the numbers. The FX/Z1's are a ways off of true 1080 recording. For example a Varicam captures only 960x720 then records this to tape in 720p, but will dust both the JVC's and Sony's!
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Old May 14th, 2005, 03:14 AM   #17
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Originally Posted by Ken Hodson
The JVC's also use a 6 frame GOP while Sony a 12 frame GOP.
That's in 50i. In 60i the Sony uses a 15-frame GOP.

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All of this math is compounded more when you consider the HD100 has the ability to shoot 24p, thus saving 1/6th more bandwidth.
Well, the jury's still out on that. There are conflicting reports of how the JVC actually records 24p. Initial reports said that it was a straight 24-frame recording, but Steve Gibby talked to the guys at Lumiere, who had actual 24p footage, and he reported that they said that instead what was happening was the JVC was recording the 24p footage within a 60p data stream. How that affects compression, I don't know -- may affect it a lot, or maybe not significantly at all, since MPEG-2 is highly skilled at detecting redundancy and saving space.

So the JVC's 24P may be even less compressed than its 30p, or it may be more compressed (due to being carried in a 60p data stream).

In the end, all that really matters is what the footage looks like once you get it into your NLE. Whether it's 1080 or 720, whether it's HDV or DVCPRO-HD, it's all up to what the final footage looks like. And that's not a question we can examine (or even think about beginning to explore) for months, from either new camera. Until then, the Sony is the only affordable HD camera around.

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Sony is obviously targeting the eager HD consummer who is attracted by the big number "1080i" while JVC is targeting the indie filmaker. Sony's market is about 100 times bigger, but JVC must find its niche somewhere or die.
Interesting angle... but I don't know that I'd agree entirely. In the circumstances I've seen HD be used, it's never been in weddings or events, and rarely in indie filmmaking (although that audience is probably the most attracted to the idea of affordable HD!). As HD is used today, it's in commercials, and corporate videos, and infomercials. And sports. And of those uses, all but sports are well suited to the 24p approach of the JVC. The indie filmmaking crowd would be a bonus, but for people actually working with HD now, for paying clients, it seems like the JVC has plenty of potential.

I think there's plenty of room for both products.
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Old May 14th, 2005, 07:58 AM   #18
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but it is the recorded resolution that matters. The Sony's use 960x1080 chips
Never mind that even 960x1080 is larger than 1280x720, and implementation of pixel shift can be expected in to increase that resolution in many situations.
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Old May 14th, 2005, 12:32 PM   #19
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"Never mind that even 960x1080 is larger than 1280x720, and implementation of pixel shift can be expected in to increase that resolution in many situations."

While interlaced and long GOP will bring it right down again. I will again point out that the Varicam captures only 960x720, but looks cleaner, sharper, better. How is that then?

Barry - It is my understanding that the cam captures everything at 60p as this is what it exports uncompressed. But it will put to tape only the frames needed. Eg. all 60 when in 480p mode, 30 or 25,24 when in 720p mode. Unless of course you seriously believe they are cramming 2X the info as the HD10 in 19Mbps? I don't think so. If they really were putting 60p to tape, where is the 720p60 mode? You don't think they would just leave it out if they were already capturing it. Of couse not.
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Old May 14th, 2005, 01:30 PM   #20
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Barry - It is my understanding that the cam captures everything at 60p as this is what it exports uncompressed. But it will put to tape only the frames needed.
No, that's backwards. A common misconception, but backwards.

The VariCam captures the frames it needs, at the appropriate scanning rate. For 60p, it will capture 60 frames per second. For 30p, it doesn't capture 60 frames and then drop half of them... instead it captures 30 frames, each spaced 1/30 of a second apart. Same for 24p -- it runs the CCD at 24Hz, captures 24 frames per second, each frame 1/24 of a second apart.

When it comes time to record to tape, it will duplicate frames to round out the sequence to 60, because the tape format can only record 60 frames per second. So for 30p, it will record each frame on the tape twice, so you get 60 frames on tape, but 30 distinct, unique frames (and each unique frame is flagged as "active", and the duplicate frames aren't, so when you use the frame rate conversion tool it can discard the duplicates). For 24p, it records using a 2:3 sequence, etc.

But it doesn't just shoot at 60fps and then drop frames -- that'd look awful. It does it the right way -- variably scanning, capturing exactly the way it should, and then just pads the frames when recording. The HVX (or any future P2 camera) won't have to do that padding thing, because it doesn't use tape, so it'll just record the active frames directly.

The JVC uses a similar variable-scanning CCD -- or at least that's how I understand it. The CCD runs at 24hz, 30hz, or 60hz. If what you suggest is how the JVC actually works (running at 60hz all the time, then dropping frames to create 24 or 30) then that would be horrible... wouldn't be much better than CineFrame 24. I certainly hope that's not the case.

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Unless of course you seriously believe they are cramming 2X the info as the HD10 in 19Mbps? I don't think so.
That's the question mark. But it wouldn't be 2x the info, because MPEG-2 can probably encode the duplicate frames in just a few bytes. Because the pad frames would be exact duplicates of existing frames, I'm sure it wouldn't really affect compression efficiency much at all.
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If they really were putting 60p to tape, where is the 720p60 mode? You don't think they would just leave it out if they were already capturing it. Of couse not.
Well, there's a reason for that. If you go back to the original HDV spec, it does specifically mention 720p/60 as an accepted HDV standard. So why no 720p/60 to tape? I saw Adam Wilt at NAB, and he cleared it up -- he said that the NTT MPEG compression chipset that JVC is using cannot handle a 60p data rate. The tape format supports it, the camera supports it, but the MPEG encoder doesn't. So you will never get 60p on tape, and you won't get 60p out the firewire either. It's a hardware limitation.

As to how they could be then encoding the 24p within a 60p stream, I don't konw -- maybe because there's only 24 source frames the chip can handle it? I really don't know. Like I said, it's conflicting information. Steve Mullen described it as 24 frames recorded discretely. Steve Gibby spoke with the people at Lumiere, who said that they had actual footage from the camera, and the 24p data was carried within a 60p stream. I don't know what the answer is. Obviously someone got it wrong.
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Old May 14th, 2005, 02:28 PM   #21
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"Well, there's a reason for that. If you go back to the original HDV spec, it does specifically mention 720p/60 as an accepted HDV standard."

Sure it does. Always has. But it would look like crap if it had to fit in 25Mbps or less.


"That's the question mark. But it wouldn't be 2x the info, because MPEG-2 can probably encode the duplicate frames in just a few bytes. Because the pad frames would be exact duplicates of existing frames, I'm sure it wouldn't really affect compression efficiency much at all."

I think you are on the right path here. Sounds reasonable. The confussion stems from the fact that you can pull 60p discreet frames from the cam head or 30 or 24 the second you hit record.
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Last edited by Ken Hodson; May 14th, 2005 at 03:06 PM.
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